Perylene-diimides (PDIs) are outstanding versatile organic chromophores. They demonstrate exceptional thermal and photochemical stability, strongly absorb visible light, and show high fluorescence quantum yields. PDIs have been utilized as industrial dyes, electronic materials, sensors, photovoltaics, and building blocks for light-harvesting and artificial photosynthetic systems. Importantly, photophysical and redox properties of PDIs can be conveniently modified through substitution in the aromatic core at the positions 1, 6, 7, and 12 (bay region). Substitutions at bay positions and expansion of the PDI core are usually carried out starting from the halogenated derivatives, particularly brominated PDIs. These are almost exclusively synthesized through bromination of perylene dianhydride (PDA) in concentrated H2SO4 upon heating, followed by imidation with amines. Usually this bromination procedure affords a mixture of di-, tri- and tetrabrominated PDIs. The dibromoperylene diimides contain 1,7 (major) and 1,6 (minor) regioisomers. Recently, purification of 1,7 regioisomer by repetitive recrystallization has been reported. Among the brominated perylene-diimides, 1,7-dibrominated PDIs are the most widely used as starting materials for a broad variety of PDI derivatives.
There is a need in the art to develop synthetic methods for the synthesis of regioselective PDIs compounds, that can provide highly pure products in high yield.